Polymorphonuclear leucocytes release a factor(s) that induces platelet aggregation and ATP release after interaction with insoluble and surface-fixed immune complexes.

We have found that human polymorphonuclear leucocytes (PMN) can be stimulated by large aggregates (heat-aggregated IgG, chemically polymerized IgG, heavily aggregated human immune complexes) and by surface-bound immune complexes (IC) to release enzymes (lysozyme, beta glucuronidase) and a factor(s) able to induce platelet aggregation and ATP release from the platelets. Surface-bound IC were most effective in stimulating the release of this factor(s). We used several substrates for their preparation: plastic-adsorbed antigen. Sepharose-coupled antigen and polymerized antigen. The platelet-aggregating factor(s) released by IC-stimulated PMN and zymosan-stimulated PMN were compared for their susceptibility to inhibition by indomethacin. Both induced a first phase of platelet aggregation that was resistant to indomethacin, but the second phase of aggregation and the release of platelet ATP were inhibited to a variable degree, more pronounced in the case of the factor(s) released after PMN-IC interaction. The lack of inhibition of the early phases of aggregation induced by our factor(s) when platelets were simultaneously exposed to indomethacin suggests that the classical, phospholipid PAF is released under these experimental conditions. Although, further experiments will be necessary to fully characterize the factor(s) involved, our observations suggest a complex interrelationship between human PMN and platelet activation, which may play an important role in the sequence of events that mediate the tissue deposition of IC and appearance of inflammatory changes.